New pre-commit-access-control.pl hook

I've done some major modifications in the commit-access-control.pl
hook, and would like to add it to the Subversion distribution to
replace the current commit-access-control.pl script. However, I am not
sure what the procedure is in order to do this.

Like the current commit-access-control.pl hook, this new version
controls who is allowed to read or write to the archive based upon the
name of the file. This is set via a Perl RegEx. Like the current
version, you set up these parameters via an MS-DOS like IniFile.

However, I've added a few more features:

* You can now define user groups and use those for file permissions.

* You can now specify three permission levels: read-only, read-write,
and add-only. This last one is for tags. Add-only allows you to define
a new tag, but won't allow you to modify the tag by checking it out
and committing the changes.

* A special group called "@ALL" signifies all users.

* You may specify <USERS> in a file regular expression. This gets
translated into the user id when making file matching comparisons.
This allows you to quickly specify permissions in special private user
directories.

* A new feature allows you to specify the property and value that
property should have on files. This allows you to verify that
properties are set correctly when a new file or directory is created
or modified.

* A new feature for revision properties has also been added. However,
this is currently limited to just "svn:log". With this feature, you
can make sure that the log comment is in the correct format.

* You can now prevent users from creating or renaming files with "bad"
filenames. For example, you can prevent spaces in filenames or from
using file names that will cause problems with either Subversion or
are illegal in MS-DOS.